Generally, bearing devices that are used for a hydraulic tractor shovel, and so on has a structure in which a boss member is disposed between a pair of left and right bracket members, and a connection pin is inserted into bushings that are fitted into the pair of bracket members and the boss member. Thus, the connection pin can rotatably connect the boss member to the bracket members.
In the case of a hydraulic tractor shovel, for example, this type of bearing device that is conventionally used is disposed in each of connection portions of a boom, an arm, a bucket and so on that compose a working apparatus. For example, in the connection portion between the arm and the bucket, a connection pin rotatably connects bracket members that are disposed in the bucket to a boss member that is disposed at the fore end of the arm.
Lubricating oil such as grease is provided between the sliding surfaces of the bushings that are fitted into the boss member and the pair of bracket members, and the connection pin to allow the boss member and the pair of bracket members to smoothly rotate. In this type of bearing device, in order to prevent a connection pin from detaching from bushings, a bearing device which includes retaining stopper plates that are arranged at the ends of a pair of bracket members has been proposed (see Japanese Patent Laid-Open Publication TOKUKAI No. HEI 11-37138).
FIG. 5 is a cross-sectional view showing a bearing device that is disclosed in Japanese Patent Laid-Open Publication TOKUKAI No. HEI 11-37138. A pair of left and right bracket members 54 protrude outward from a bucket of a hydraulic tractor shovel (not shown). An arm boss 52 is arranged between the pair of brackets 54. A first bushing 55 is fitted in a bushing fit opening 52A of the arm boss 52. A sliding surface 55A that is in slidable contact with a connection pin 59 is formed on the inner peripheral surface of the first bushing 55. Sealing members 56 are attached between the arm boss 52 and the connection pin 59. Thus, the aforementioned sliding surface 55A is sealed by the sealing members 56.
Second bushings 57 are fitted in bushing fit openings 54A of the aforementioned pair of bracket members 54. Sliding surfaces 57A that are in slidable contact with the connection pin 59 are formed on the inner peripheral surfaces of the second bushings 57. Sealing members 58 are attached between the bracket members 54 and the connection pin 59. Thus, the aforementioned sliding surfaces 57A are sealed by the sealing members 58.
Annular plates 54B are fastened on the inner side surfaces of the bracket members 54 that are opposed to the arm boss 52. A pair of stopper plates 60 that retain the connection pin 59 are attached on the outer side surfaces of the bracket members 54.
The connection pin 59 is formed in a predetermined axial length that is shorter than the distance between the outer side surfaces of the bracket member 54. An axial middle part of the connection pin 59 is slidably inserted into the first bushing 55. Both axial end parts of the connection pin 59 are slidably inserted into the second bushing 57. An axial oil channel 59A and a plurality of oil channels 59B are formed inside the connection pin 59. The both ends of the oil channel 59A are communicated to a pair of oil storage chambers 62. The oil channels 59B radially extend from the oil channel 59A.
The aforementioned stopper plates 60 are tightly attached on the outer side surfaces of the bracket members 54 by a plurality of bolts 61. The pair of left and right stopper plates 60 close the bushing fit openings 54A of the bracket members 54 so that the connection pin 59 is held in a retained state in the first and second bushings 55 and 57. An annular oil groove 60A and an O-ring groove 60B are formed on the inner side surface of each stopper plate 60 that is in contact with the bracket member 54. The O-ring groove 60B is located on the outer peripheral side relative to the annular oil groove 60A.
The oil storage chambers 62 are formed between the pair of left and right stopper plates 60, and the ends of the connection pin 59. The oil storage chambers 62 store the lubricating oil that is provided between the sliding surfaces 55A and 57A of the first and second bushings 55 and 57, and the connection pin 59. An O-ring 66 is disposed between the arm boss 52 and the annular plate 54B of each bracket member 54.
The lubricating oil that is stored in the pair of oil storage chambers 62 is provided to the sliding surfaces 57A where the connection pin 59 is in slidable contact with the second bushing 57 from the both end of the connection pin 59, and is provided to the sliding surfaces 55A where the connection pin 59 is in slidable contact with the first bushing 55 through the oil channels 59A and 59B of the connection pin 59. The lubricating oil is fed through an oil feed channel 52B after an oil feed nipple 53 is detached. Thus, the lubricating oil is added to the pair of oil storage chambers 62 through the oil channels 59A and 59B.
In the bearing device disclosed in Japanese Patent Laid-open Publication TOKUKAI No. HEI 11-37138, the lubricating oil is fed through the oil feed channel 52B after the oil feed nipple 53 is detached. A part of the fed lubricating oil passes through the oil channels 59B and 59A, and is stored in the oil storage chambers 62. The stored lubricating oil is provided from the oil storage chamber 62 to the sliding surfaces 57A. Another part of the lubricating oil that is fed through the oil feed channel 52B passes through the sliding surface 55A to reach the sealing members 56.
However, the clearance between the sliding surface 55A and the connection pin 59 is narrow. In addition, this clearance is closed as a blind channel by the sealing members 56. Accordingly, the fed lubricating oil is unlikely provided to the sealing member 56 through the sliding surface 55A, and is more likely provided to the pair of oil storage chambers 62 through the oil channel 59A that is communicated to the oil feed channel 52B, and the oil channels 59B. For this reason, if the lubricating oil is added through the oil feed channel 52B at a higher pressure, the lubricating oil passes through the sliding surfaces 57A to reach the sealing members 58, and as a result leaks through the sealing members 58. Consequently, the lubricating oil leaks out from the aforementioned O-rings 66. This causes a problem.